The present invention relates to an installation for transferring a fluid between a transport vessel and a fluid reservoir on a fixed structure, of the type comprising:                a conduit which is for transporting the fluid towards the fixed structure and which is at least partially submerged in a body of water;        a device which is for conveying fluid between the vessel and the transport conduit and which is connected to a connection end of the transport conduit; and        a floating platform which is for securing the vessel and which is positioned beside the connection end and which is locally movable in the body of water, the floating platform comprising:                    a carrier structure which is intended to be partially submerged in the body of water, the carrier structure comprising an open-work trellis which delimits internal spaces which are for circulation of water and which are intended to open in the body of water,            flexible lines for anchoring the structure to the bottom of the body of water;            means for fixing lines for securing the vessel to the carrier structure.                        
The present invention is used particularly for transferring liquid hydrocarbons, such as liquefied gases, such as liquefied natural gas (LNG) or liquefied petroleum gas (LPG) between a transport vessel and a fixed structure. That fixed structure is, for example, a liquefaction unit or a gasification terminal during the charging of the vessel or a fluid reservoir during discharge thereof.
Taking into account some constraints, concerning safety and movement of the vessels, it is preferable to carry out the operations for transferring fluid with the vessel being kept outside a port, in relatively deep waters, for example, several hundreds of meters away from the coast.
In order to carry out such operations on the open sea, there are known in particular stations for charging or discharging vessels comprising a platform for transferring fluid that is fixed to the sea bed by a fixing structure which is positioned on the sea bed and which is referred to as a “jacket”. The platform supports articulated fluid transfer arms which are intended to be connected to traverse systems of the vessel which are referred to as “manifolds” on the vessel.
The known charging stations further comprise an assembly of “dolphins” in order to absorb the docking energy of the vessel and to secure it after its docking. The dolphins are also fixed to the sea bed by rigid metal piles.
The fluid transfer platform is connected to a reservoir located on the coast or on a fixed platform at sea via a flexible conduit or a pipeline which is partially or completely submerged.
This type of transfer station requires a sufficient depth of water for the draught of the vessel. Nevertheless, when the vessel is secured to the dolphins, it is not free to become orientated with respect to the elements. Without adequate protection against the swell which is generally ensured by a barrage, the relative movements between the vessel and the charging station are further very substantial. The forces applied to the securing lines between the vessel and the dolphins are therefore great, which means that the transfer station must be positioned in a sheltered site.
In order to overcome this problem, US 2004/0216485 describes a transfer installation of the above-mentioned type, in which the dolphins are replaced by semi-submersible open-work assemblies which are anchored to the sea bed by means of flexible anchoring lines.
The semi-submersible assemblies are positioned remote from the charging platform at one side and the other thereof in order to secure the front and the rear of the vessel, respectively. Those carrier structures are massive because they comprise pillars having a diameter of approximately 10 meters and struts having a contact surface-area with the water which is very large in relation to the overall volume of the structure.
In this manner, the carrier structures have substantial inertia, when they are connected to the vessel by the securing lines, so that the assembly constituted by the structure and the vessel absorbs the swell in calm weather.
However, such an installation is not entirely satisfactory. Since the carrier structure is dynamically heavy, it may have significant inertia in relation to the inertia of the vessel which is secured thereto, taking into consideration the high mass of the water which loads it and the high contact surface-area with respect to the body of water in which it is floating. The high constraints therefore continue to be applied to the securing lines between the vessel and the carrier structures.
Although the carrier structures further allow the swell to be absorbed in calm weather owing to their weight, they still remain very sensitive, owing to the large contact surface-area thereof with the water, to waves or the swell over the body of water under very poor weather conditions, in particular when the swell is greater than six meters. Consequently, the securing lines of the carrier structures must be over-dimensioned in order to withstand the swell in the case of rough weather.